System and methods for antenna optimization for wireless broadband communication

ABSTRACT

A system and method for antenna optimization for wireless broadband communication is provided. Such an enhanced antenna array includes higher-gain antenna and lower-gain antenna. The beamforming antenna, both higher-gain and lower-gain, are designed to be able to transmit to and receive from another transceiver. The higher-gain antenna may be designed to form a more directional beam substantially closer to the horizon; whereas the lower-gain antenna is capable of forming a less directional beam at a distance further from the horizon. In both cases, the antenna may form their respective beams anywhere in the 360 degrees horizontally around the antenna array. The higher-gain antenna may include a coverage area from the horizon to a substantially acute angle from the horizon in the vertical direction. In contrast, the lower-gain antenna may have coverage from the substantially acute angle from the horizon to substantially vertical. The substantially acute angle may be approximately 10 degrees in some cases. In some cases the lower-gain antenna may include four elements. Likewise, in some embodiments, the higher-gain antenna may include four elements as well.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to provisional application No.61/213,999 filed Aug. 6, 2009, entitled “Broadband WirelessCommunication”, by Michael Leabman, which is incorporated by referenceherein for all purposes.

Further, this application claims priority to provisional application No.61/272,001 filed Aug. 10, 2009, entitled “MAC and Antenna Optimizationsfor Long-Distance Wireless Communication”, by Michael Leabman, which isincorporated by reference herein for all purposes.

Additionally, this application is related to co-pending application Ser.No. 12/830,324, filed Jul. 4, 2010, entitled “System and Methods forWireless Broadband Delivery of Data”, by Michael A. Leabman, which isincorporated by reference herein for all purposes.

Additionally, this application is related to co-pending application Ser.No. 12/830,326, filed Jul. 4, 2010, entitled “System and Methods forSimultaneous Wireless Broadband Communication Between Multiple BaseStations”, by Michael A. Leabman, which is incorporated by referenceherein for all purposes.

Additionally, this application is related to co-pending application Ser.No. 12/830,328, filed Jul. 4, 2010, entitled “System and Methods forScalable Processing of Received Radio Frequency Beamform Signal”, byMichael A. Leabman, which is incorporated by reference herein for allpurposes.

Additionally, this application is related to co-pending application Ser.No. 12/830,239, filed Jul. 4, 2010, entitled “System and Methods forMedia Access Control Optimization for Long Range WirelessCommunication”, by Michael A. Leabman, which is incorporated byreference herein for all purposes.

BACKGROUND

The present invention relates to data delivery systems and methods. Moreparticularly, the present invention relates to systems and methods fordelivering data content over unlicensed radio frequency (RF) spectrumbetween airborne platform and surface base stations. In someembodiments, this data delivery system may provide data at highthroughput data rates exceeding 100 Mbps to enable the transfer of awide variety of safety, operational and passenger data.

Communication and information access is imperative to the aviationindustry. Earliest commercial aircrafts had primitive voicecommunication with ground personnel over two way shortwave radio. Notonly did this communication dramatically improve flight safety, it alsoenabled accelerated commercialization of air transport on a level notpreviously known.

Since then, airborne platform have been further upgraded with advent ofradar, computers, and even data links to further improve communications.These technologies serve to improve in-flight safety and provideamenities to passengers. However, true broadband high-throughput datauplinks are typically lacking for the airline industry. This is due to acombination of technical and financial constraints which havehistorically made it impractical, or even impossible, to supply high bitrate data connectivity to an entire fleet of commercial airliners.

However, regardless of hurdles, there is a need to enable broadbandwireless communication for airborne platform. This need may generally bebroken down into operational needs (i.e., maintenance and repair), airsafety needs, and passenger generated needs.

Operational (maintenance) needs are driven by cost savings the airlinemay recapture by knowing, real-time, the condition of the airborneplatform. Gigabytes of flight data are accumulated for each flight butare not easily accessible until after the airborne platform has landed(or are even totally inaccessible if not stored or later retrieval).This renders real time engine trends, fuel consumption rates, and partsperformance variances unavailable for timely repairs and cost savings.Some of this data is often discarded because downloading the datacurrently is too slow or too expensive. In newer aircrafts, such as theBoeing 777 or the Airbus 380, some such operational data may be providedon a real time basis to ground personnel in some cases; however, thisdata is often limited and relies upon low bit rate speeds. Generally,important operational data is collected and downloaded via a wiredaccess port when the airborne platform has landed. This data collection,however, is not real time data, and cannot be utilized to preplanmaintenance needs.

Safety needs include the ability to identify causes and possibly preventdisastrous accidents. Currently, the flight recorder (i.e., “Black Box”)of an airborne platform is accessible after a airborne platform crash. ACockpit Voice Recorder (CVR) is an audio recorder which is often veryuseful in identifying causes of the accident. Further, depending uponcrash location, the flight recorder and/or CVR are often never found.Without the flight recorder and/or CVR, it may be impossible todetermine what caused the crash. Besides satisfying public curiosity andaiding the bereaved, this causal data is very important in generatingprotocols and/or safety inspections to prevent future similar accidents.Likewise, if critical airborne platform conditions were known by groundpersonnel in real time, potential disasters could possibly be identifiedand addressed before they happen. These safety needs are currently unmetgiven current limited data bandwidth to aircrafts.

Lastly, there are a number of passenger generated needs for larger databandwidth. For example, unfettered Internet access for passengers couldgenerate high advertising revenues. Likewise, high-speed Internetsurfing would facilitate more passenger purchases and commissions forairlines. The limited internet access currently offered by airlinesdiscourages use due to its slow speeds and relative cost.

Those airborne platform that are equipped to provide Internet access, ordata communication, typically do so at little more than dial-up speeds.This is due, as stated earlier, to current technological and financialhurdles. One simple approach would be to purchase licensed radiofrequency (RF) spectrum to devise a dedicated surface to airborneplatform communication network. However such a system would requiressubstantial spectrum to service an airline fleet and is thus financiallyprohibitive. For example, it is expected that 160 MHz of spectrum wouldbe required to achieve the desired performance. A recent purchase byVerizon of 14 MHz cost the company between one and two billion dollars.Of course some spectrum is more valuable than others depending uponservices envisioned. Cellular and close to cellular spectrum isconsidered prime spectrum real estate. Regardless, the purchase of thenecessary licensed RF spectrum would require an exorbitant capitalinvestment extending to several billions of dollars.

Other approaches to providing data connectivity to aircrafts are toinstall Satellite Ku Band or Cellular receivers. The weight of aSatellite system is roughly 450 pounds. A cellular system may weighless, but is still a substantial 125 pounds of excess weight. Weight inan airborne platform is directly related to further fuel consumption.Thus, these systems may cost the airline a lot over the course of theirusable lifetimes.

In addition to fuel costs, the units themselves are costly. The cellularsystem has a substantial cost in the neighborhood of one hundred andtwenty five thousand dollars upfront per airborne platform. The cost fora satellite system may be even larger at around four hundred and fiftythousand dollars. Additionally, the cost of maintenance for thesatellite system may tack on an additional hundred thousand dollars orso per year per airborne platform, and the array on the airborneplatform may, in some cases, extract a substantial aerodynamic penalty.

Additionally, the operational costs of these devices may be very largebased upon the size of data being transmitted. It may be costly to sendsizable data over satellite or cellular systems.

Lastly, the data rates for common, shared service commercial systems arestill relatively low; satellite operates at roughly 1.5 Mbps perairborne platform, and Cellular systems operate between 0.25 and 2.0Mbps. Further, signal reliability may be of issue for cellular systems.Likewise, satellite bandwidth may be overwhelmed by sudden surges indata download demand, such as may occur if a large number of passengerson a number of airborne platform start data intensive downloads.

Thus, data must be limited in these cases to the point where only afraction of the above noted needs are capable of being met. For example,the time needed to download a two hour movie may exceed three hoursgiven these technologies. Thus, the existing technologies for datatransfer to a airborne platform are woefully inadequate to meet theairlines' needs, even when the funds are available to implement them.

In view of the foregoing, systems and methods for long distance wirelessdelivery of data are disclosed. The present invention provides a novelsystem for providing data to or from aircrafts at unprecedented datarates, and in a cost effective manner.

SUMMARY

The present invention discloses a data delivery system. Moreparticularly, the present invention teaches systems and methods forantenna optimization for a wireless broadband communication between anairborne platform and terrestrial base station. The optimized antenna,in some embodiments, may be utilized to provide high speed datatransmission to airborne platforms over a long distance in a costeffective manner.

In one embodiment, the system and method for antenna optimization forwireless broadband communication includes an enhanced antenna arraywhich includes higher-gain antenna and lower-gain antenna. Thebeamforming antenna, both higher-gain and lower-gain, are designed to beable to transmit to and receive from another transceiver.

The higher-gain antenna may be designed to form a more directional beamsubstantially closer to the horizon; whereas the lower-gain antenna iscapable of forming a less directional beam at a distance further fromthe horizon. In both cases, the antenna may form their respective beamsanywhere in the 360 degrees horizontally around the antenna array. Wherethey differ is their respective coverage areas in the verticaldirection, in some embodiments.

As noted, the higher-gain antenna may form a beam closer to the horizon.This may include a coverage area from the horizon to a substantiallyacute angle from the horizon in the vertical direction. In contrast, insome embodiments, the lower-gain antenna may have coverage from thesubstantially acute angle from the horizon to substantially vertical.The substantially acute angle may be approximately 10 degrees in somecases.

In some embodiments, this enables coverage of the antenna array in 360degrees horizontally, and 180 degrees from horizon to vertical. Thiscomplete coverage is further refined by having higher gain near horizonand lower gain as angles are more vertical.

Also note that in some cases the lower-gain antenna may include fourelements. Likewise, is some embodiments, the higher-gain antenna mayinclude four elements as well. In other cases, more or fewer elementsare considered as within the scope of some embodiments.

Note that the various features of embodiments of the present inventiondescribed above may be practiced alone or in combination. These andother features of various embodiments of the present invention will bedescribed in more detail below in the detailed description of theinvention and in conjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is an example illustration of an airborne platform in wirelessbroadband communication with a plurality of surface based antenna arrayscoupled to base stations, in accordance with some embodiments;

FIG. 2 is an example illustration of more than one airborne platform inwireless broadband communication with a plurality of surface basedantenna arrays, in accordance with some embodiments;

FIG. 3 is an example illustration of an airborne platform orienting anull space on an interference source while in wireless broadbandcommunication with a surface based antenna arrays, in accordance withsome embodiments;

FIG. 4 is an example illustration of an antenna arrays projecting anumber of synchronization beamforms, in accordance with someembodiments;

FIG. 5 is a detailed example illustration of an airborne platform inwireless broadband communication with a surface based antenna arrayincluding antenna panels, in accordance with some embodiments;

FIG. 6 is a logical example illustration of an antenna array panel, inaccordance with some embodiments;

FIG. 7A is an example illustration of a broad coverage antenna inaccordance with some embodiments;

FIG. 7B is an example illustration of a squinted broad coverage antennain accordance with some embodiments;

FIG. 8 is an example block diagram of a scalable architecture for thedata delivery system in accordance with some embodiments;

FIG. 9 is an example flowchart diagram for the process of deliveringdata over a wireless broadband data delivery system in accordance withsome embodiments;

FIG. 10A is a first example flowchart diagram for the process ofsynchronizing a surface based antenna array with a mobile antenna arrayin accordance with some embodiments;

FIG. 10B is a second example flowchart diagram for the process ofsynchronizing a surface based antenna array with a mobile antenna arrayin accordance with some embodiments;

FIG. 11 is an example flowchart diagram for the process of training asurface based antenna array with a mobile antenna array in accordancewith some embodiments;

FIG. 12 is an example flowchart diagram for the process of generating anull space to block an interfering signal in accordance with someembodiments;

FIG. 13 is an example flowchart diagram for the process of balancingcommunication loads between multiple base stations in accordance withsome embodiments;

FIG. 14 is an example illustration diagram of the vertical airspacearound an antenna array in accordance with some embodiments; and

FIGS. 15A and 15B are example illustrations of directional beamformingby an antenna array in range of a target and interference source inaccordance with some embodiments.

DETAILED DESCRIPTION

The present invention will now be described in detail with reference toselected preferred embodiments thereof as illustrated in theaccompanying drawings. In the following description, numerous specificdetails are set forth in order to provide a thorough understanding ofthe present invention. It will be apparent, however, to one skilled inthe art, that the present invention may be practiced without some or allof these specific details. In other instances, well known process stepsand/or structures have not been described in detail in order to notunnecessarily obscure the present invention. The features and advantagesof the present invention may be better understood with reference to thedrawings and discussions that follow.

As previously disclosed, in order to provide a system that is capable ofmeeting the load demands of the airline industry, and not beprohibitively expensive, a number of conditions must be met. Theseinclude utilization of unlicensed spectrum in some embodiments,sufficient data throughput, and sufficient range. In other embodiments,licensed radio spectrum is also considered a viable medium for use bythe broadband wireless communication system.

In order to meet these requirements at reasonable costs, someembodiments relating generally to systems and methods for long rangewireless delivery of data over Radio Frequency (RF) spectrum areprovided. In some embodiments, it may be desirable to utilize unlicensedspectrum for the system for cost saving purposes. Unlicensed spectrum inthe United States includes spectrum centered around 2.45 GHz and 5.8GHz, for example. These regions are under the jurisdiction of theFederal Communications Commission (FCC). The FCC regulation Part 15 (47CFR §15) dictates how unlicensed spectrum may be utilized, including apower envelope that any device operating in this spectrum must complywith. The FCC Part 15.247 restricts power to 1 watt EIRP with a 6 dBiAntenna. As antenna gain increases, the total allowed EIRP must belowered according to the part 15.247 spec. For example, below isprovided a table overview of some of the current regulations of FCC Part15:

TABLE 1 FCC Part 15 Max. Ant. Transmitter RF gain EIRP Permissible underPart 15: power (dBi) (W) 900 MHz 30 dBm (1 W) 6 3.98 2.4 GHz omni- 30dBm (1 W) 6 3.98 directional 2.4 GHz directional 29 dBm (800 mW) 9 6.3528 dBm (640 mW) 12 10.14 27 dBM (500 mW) 15 15.81 26 dBm (400 mW) 1825.23 25 dBm (320 mW) 21 40.28 24 dBm (250 mW) 24 62.79 23 dBm (200 mW)27 100.2 22 dBm (160 mW) 30 160.0 5.15-5.25 GHz 16 dBm (40 mW) 0 0.165.25-5.35 GHz 23 dBm (200 mW) 6 0.80 5.725-5.825 GHz omni- 30 dBm (1 W)6 3.98 directional 5.725-5.825 GHz directional+ 30 dBm (1 W) 28 630.9

While the some embodiments utilize unlicensed radio spectrum, it is alsoconsidered within the scope of some embodiments that other surfacewireless signal may likewise be utilized for transmission of data inthis manner, such as licensed radio spectrum.

In some embodiments, the usage of beamforming on the radio spectrum isutilized to achieve the necessary range and data transfer rates needed.In addition, by null steering, potential interference sources may beignored. This enables a system with higher fidelity, range, and datarates for substantially less capital investment than satellite orcellular systems.

The broadband wireless communication system 200 may be used to provide adata communication link to airborne platform 102 a and 102 b. This linkmay be used to provide data networking for multiple users located on theairborne platform. For example, the airborne platform 102 a may use adevice to communicate with one or more base stations 110 a. Thisconnection may then be shared with a variety of users includingpassengers on board the airborne platform 102 a and 102 b.

This broadband wireless communications link may be used for a widevariety of services including one or more of the following, alone or inany combination: airborne platform entertainment, such as, for example,audio and/or video streaming, Internet access, on-demand movies, and thelike; airborne platform security system operation, such as, for example,streaming real-time cockpit/passenger cabin video and/or audio to/fromthe surface, flight tracking, communications between flight crews andthe ground, and the like; providing information services, such as, forexample, integrating a terminal wireless system (i.e., the same systemthat downloads content at the gate); travel-related services (such ashotel, car, restaurant, and/or flight reservations); high-speed Internetaccess for airborne platform passengers; and so on.

Furthermore, a single communication link to surface may be shared withother systems on the airborne platform 102 a and with passengers usingany data networking technology, including a WiFi network, Ethernetconnections, and the like. Services may be hosted on the airborneplatform 102 a using this data networking technology either alone, or incombination with the surface communication link. For example, in someembodiments, the airborne platform 102 a may include a gaming serverthat is activated upon entering airspace that is not subject to gaminglaws and regulations. In this manner, passengers may access the gamingserver and place wagers, play casino-like games (e.g., slot machines,blackjack, video poker, and the like). In some embodiments, thecommunication link is used, for example, to verify financialinformation, to transfer money, and the like. Some implementations usePayPal or other Internet payment service to effect such transfers.

Note that in the remainder of this application, particular attentionwill be placed upon transmission of data to and from an airborneplatform. It is intended, however, that some embodiments be adapted foruse for a wide variety of long range data transmission applications. Forexample, the provided long range wireless communication system andmethods may be equally well suited for use in maritime applications suchas cargo and cruise ships, for locomotive data transfer, such as cargo,commuter and high speed trains and/or for stationary data locations,such as off-grid homes or the like. Stationary and mobile surfaceplatforms, e.g., ground stations, ships, trains, can communicate witheach other via public and/and private networks such as the Internet andPOTS, and combinations thereof. These networks can be implemented usingwired and/or wireless links such as microwave or shortwave links, andcombinations thereof. In addition to long-range air to/from groundwireless communications, exemplary embodiments described in detailbelow, the present invention may also be adapted to ground to groundwireless communications.

The following description of some embodiments will be provided inrelation to numerous subsections. The use of subsections, with headings,is intended to provide greater clarity and structure to the embodiments.In no way are the subsections intended to limit or constrain thedisclosure contained therein. Thus, disclosures in any one section areintended to apply to all other sections, as is applicable.

I. Wireless Broadband Data Delivery

In some embodiments, at FIGS. 1 and 2, a broadband wirelesscommunication system 200 enables data communication with one or moreAirborne platform 102 a, 102 b and 102 c. Airborne platform 102 a, 102 band 102 c communicate with one or more Antenna Arrays 104 a, 104 b, and104 c across a wireless link 106 a, 106 b, 106 c, 106 d, 106 e and 106f. In some embodiments, the wireless link 106 a, 106 b, 106 c, 106 d,106 e and 106 f may include directional signal propagation generatedfrom phased antenna arrays 104 a, 104 b, and 104 c. Such a technique isknown in the art as “beamforming” and will be discussed in considerabledetail below.

Adaptive signal processing, such as that utilized for the beamformingdiscussed in this application, uses an array of elements, and has longbeen a solution to the problem of combating interference signals incommunication systems. However, with the introduction of compact,inexpensive digital computers, and novel and sophisticated protocols, itis now feasible to implement more complicated results from detection andestimation theory. These results enable adaptive array systems which arecapable of adjusting and responding to rapid changes in the signalenvironment. As a consequence, these systems have much greaterflexibility, reliability, and improved reception over prior adaptivearray systems.

Where common filter techniques using one element have proven to beeffective when frequencies of interest differ from the frequencies ofinterference signals, adaptive array algorithms are required when thespectrum of interference signals and the desired signal overlap. Anadaptive array has the ability, when properly implemented, toautomatically sense and separate signals and interference noise fromdifferent directions without prior knowledge of the environment.Further, adaptive arrays may be utilized in conjunction with otherinterference reduction techniques, thus achieving a reduction ininterference at a greater level than could be achieved using any onemethod.

In conventional communication systems, a direct sequence spread spectrumsystem is often utilized, modulating the communication signal with apseudonoise (PN) signal and later dispreading it with the original knownPN sequence. While this conventional method can reduce interference, itis limited by the length of the PN sequence. The longer the PN code, thegreater the ability to separate the signal from interference noise.However, since longer PN sequences also result in longer transmissiondelays, the length of the PN code, and thus the ability to cancel noise,is often limited. As this is frequently the case, another method, suchas an adaptive array system, is often implemented in conjunction withthe spread-spectrum approach when further interference attenuation andgreater channel capacity is needed.

While classical adaptive array methods have proven to be very effectivefor cancellation of interference signals, they are still plagued byseveral severe limitations. The ability of such a system to cancelinterference signals is strongly influenced by the arrival angle andbandwidth of the interference signals. To alleviate these problems, anadaptive system, one which applies multiple frequency-dependent weightsto each array element rather than just one weight to each element, maybe utilized in order to achieve numerous benefits over the older, moreclassical approaches. This approach known as adaptive band-partitioning,divides the frequency spectrum into multiple narrow frequency bins, andthen performs spatial cancellation on each bin. The primary advantage ofthis approach is the ability to cancel interference signals ofappreciable bandwidths. Furthermore, the system also has the ability tocancel a greater number of narrowband interference signals. While theclassical approach is capable of attenuating N−1 narrowband interferencesignals, N being the number of antenna elements in the array, the newproposed system has the ability of attenuating N−1 narrowbandinterference signals in each frequency bin.

Each Airborne platform 102 a may include its own wireless communicationsystem including an antenna array 104 a and processing capabilities.Further, the Airborne platform 102 a may function as a platform foradditional mobile devices, such as media players, gaming systems, videodevices and the like.

The surface based Antenna Arrays 104 a, 104 b and 104 c are coupled to aLocal Base Stations 110 a, 110 b and 110 c, respectively. Each BaseStation 110 a, 110 b and 110 c may supply the processing requirementsfor directional data transmission at the Antenna Arrays 102 a, 102 b and102 c, as will be described in greater detail below.

The Local Base Stations 110 a, 110 b and 110 c may be connected to anetwork 108, such as, for example, the Internet. Connection of the LocalBase Stations 110 a, 110 b and 110 c to the Network 108 may beaccomplished via a wired connection, wirelessly (i.e., radio signal,microwave signal, etc.), or through any reasonable combination. Threebase stations 110 a, 110 b and 110 c are shown in FIGS. 1 and 2;however, any number of base stations 110 a, 110 b and 110 c may be used.For example, a high-capacity system covering the continental UnitedStates may include approximately 50-500 base stations 110 a, 110 b and110 c and Antenna Arrays 104 a, 104 b and 104 c strategically locatedbased on customer utilization and demands. Of course more or fewer basestations may be utilized depending upon infrastructure and saturationrequirements.

The Network 108 may also couple to a Centralized Processing Center 112which may provide greater coordination of Base Station 110 a, 110 b and110 c management. Likewise, the Centralized Processing Center 112 maylikewise collect and host information and data for the airborneplatform.

A broadband wireless communication system enabling broadband wirelesscommunications with airborne platform 102 a and 102 b can be implementedusing cellular, sectorized Antenna Arrays 104 a, 104 b and 104 c thatare tied to a network 108 via Base Stations 110 a, 110 b and 110 c, suchas, for example, the public switched telephone network (“PSTN”), aprivate network, the Internet, and the like. Antenna Arrays 104 a, 104 band 104 c frequency allocations may be made according to widely knowntechniques used in mobile telecommunications; however, an airborneplatform flying only 10,000 feet in the sky has line-of-sight radiocoverage of over 120 miles in every direction. Accordingly, an airborneplatform is likely to be capable of line-of-sight communications withmultiple Antenna Arrays 104 a, 104 b and 104 c. Furthermore, twoairborne platform 102 a and 102 b flying at 10,000 feet may be able toconduct line-of-sight communications over a distance of 240 miles. Asaltitude increases, the aircrafts' 102 a and 102 b line of sightcommunications range increases.

To improve the spectral efficiency of the broadband wirelesscommunication system, it is desirable to use directional antennas.Directional antennas use multiple antennas in each Antenna Array 104,each antenna is fed the same foundation signal but that signal isaltered for some antennas by changing the phase and sometimes both phaseand amplitude to generate directional transmissions. This spatialselectivity is achieved by using adaptive or fixed receive/transmit beampatterns. This is known in the art, as noted above, as beamforming.Beamforming may be utilized to send data signals a large distance to thetarget with considerable effective power (gain).

Traditionally, beamforming has been limited in its effectiveness. Forexample, the use of beamforming on rapidly moving devices, such as anairborne platform, is known to be difficult due to Doppler Effects.Likewise, the added benefit in gain by utilizing beamforming is notrealizable in traditional systems because in these systems the abilityto synchronize the two communicating antenna arrays is limited to thecoverage area of a single antenna transmitting in an omnidirectionalfashion.

Embodiments overcome these technological hurdles by enabling beamformsynchronization protocols, enhanced handling of Doppler Effects, nullsteering and other means of enabling efficient and effective usage of abeamforming data communication system in conjunction with airborneplatform.

In some embodiments, the surface based antenna array 104 a may includefour or more antennas. Likewise, the antenna array located at theairborne platform may consist of four or more antennas. This may becontrasted with typical WiMAX and LTE systems which merely employ twoantennas on the receiving end, and a single antenna for transmission. Inthis embodiment, all four of the array antennas are utilized for bothtransmission and receiving. Note that surface based includes any surfacebased, or sea based system. Further a surface based system may bestationary, such as an installation base station, or mobile, such as abase station on a ship or locomotive.

Having four antennas enables the arrays to project four beamforms,exhibit four distinct desired nulls, or a combination thereof as will bedescribed in greater detail below. Of course, in other embodiments, moreor fewer antennas may be included in the arrays on the surface and onthe airborne platform. Note that a system, such as that described inthis embodiment, may have a functional range of over 100 miles with datarates of 100 Mbps entirely as a consequence of antenna performancewithout an increase in delivered power to the antenna.

Further, while in some embodiments the airborne platform antenna arrayhas the same number of antennas as the surface based array 104 a, it isconsidered that different number of antennas may be utilized by eacharray as is desired. For example, in a crowded region in which a largenumber of airborne platform travel, such as near an airport, it may bedesirous for the surface based antenna arrays to include more than fourantennas, as this enables the array to generate a larger number ofbeams, thereby enabling the surface array 104 a to maintaincommunication with more airborne platform at a time.

An additional benefit of some embodiments is the ability to formrelatively narrow beamforms. In some cases these beams may achievenearly 5-10 degrees of coverage. This means that for any given antennaarray 104 a there is theoretically up to 72 discrete non-overlappingdirections of beamforming in the horizontal direction (360°/5°=72).Likewise, in the vertical direction there are up to 18 beamstheoretically possible (90°/5°=18). Thus, at any given time, the threedimensional space existing around an antenna array 104 a could,conceivably, be segmented into 1296 discrete, non-overlapping volumesgiven a beam width of five degrees (72×18=1296).

As beam width increases, however, the coverage of the area around theantenna array 104 a becomes less granular. For example, for beamforms of10 degree coverage, there are theoretically 36 discrete non-overlappingdirections of beamforming in the horizontal direction, and only nine inthe vertical direction. This results in a far fewer 324 discrete,non-overlapping volumes around the antenna array 104 a. Thus, eventhough the beam coverage is simply double that of a narrow five degreebeam, there are four times fewer volumes individually perceivable aroundthe antenna array 104 a.

Turn briefly to FIG. 14 which illustrates a vertical area of airspacearound an antenna array 104 a. Here distance from the array 104 a isshown to 100 miles. Likewise, vertical altitude is shown between 10,000feet and 60,000 feet. Typical airborne platform travel at altitudesbetween 10,000 feet and 60,000 feet under normal conditions. Note thatthe present illustration is not to scale to provide greater readability.

Also illustrated at this example, figure is a segmentation of the areain the vertical direction by ten degree increments. Thus, it isillustrated how the vertical area is divided into discrete,non-overlapping areas. Now, envision looking directly down upon theantenna array 104 a. The array would be visible as a point at the centerof a 100 mile circle prescribing the range of the antenna array 104 a.This horizontal area may be sectioned by beamform coverage angles, inthis example by 10 degree increments, like a pie. Combining this pieimage with the vertical areas illustrated by FIG. 14 provides anapproximation of the number of discrete volumes (i.e., granularity) ofcoverage that the given array 104 a is capable of producing.

As airborne platform 102 a, 102 b and 102 c fly, the relative directionfrom the airborne platform 102 a, 102 b and 102 c to the base stations'antenna array 104 a, 104 b and 104 c changes. Accordingly, it isdesirable to be able to change the direction in which RF emissionsradiate. Many such techniques are known in the art, for example, one ormore directional antennas may be used. These directional antennas may bemechanically positioned to transmit in the desired direction.Alternatively, a set of directional antennas may be used, with atransceiver switching between the available antennas to select asuitably-oriented antenna. Further, in some embodiments, a smart antennaarray 104 a is used to dynamically vary directivity of transmissionand/or reception.

In some implementations, some of the base stations 110 a, 110 b and 110c may not have direct connections to the network 108. For example, ifbase station 104 a is deployed in a remote location where Internetaccess is expensive, unreliable, inconvenient, or otherwise undesirable,the base station 110 a may instead be deployed with a wireless link tothe network 108. This wireless link may be implemented using thebroadband wireless techniques disclosed herein or using any other datacommunications technology now known or later developed.

In one implementation, the base stations 110 a, 110 b and 110 c areconnected to the network 108 through one or more of the following: (i) awireless communications link using the same spectrum and technology aswireless links 106 a, 106 b, 106 c and 106 d; (ii) parabolic microwavesignaling; (iii) the internet; (iv) the public switched telephonenetworks (“PSTN”); (v) a private network; and (vi) any combinationthereof. Additionally, in most implementations, it is desirable toprovide surface-based base stations 104 a, 104 b and 104 c; however, thesystems and techniques described herein would be equally applicable to asystem using one or more airborne base station 104 a, 104 b and 104 c.For example, a base station 104 a, 104 b and 104 c may be used as anairborne mobile command center.

As noted previously, for purposes of example, airborne platforms 102 aand 102 b are referenced as mobile devices for purposes of example only.One skilled in the art will appreciate that the systems and techniquesdescribed herein are equally applicable to other fixed and mobiledevices. For example, the techniques described herein may be used toenable broadband wireless data communications for automobiles, marinevessels, trains, and the like.

In some embodiments, it may be desirable for the radio system to havethe ability to switch between multiple power sources. For example, aradio device in an airborne platform may be configured to switch betweena battery backup, and an at-gate power source.

Attention will now be turned to FIG. 9, where an example illustration ofan embodiment of the process for wireless broadband communication isprovided. As both the surface based antenna array 104 a and the antennaarray in the airborne platform 102 a are equally capable of bothtransmission and receiving, the process as laid out in FIG. 9 may, insome embodiments, apply equally well to the system of the surface basestation (with corresponding antenna array), or the mobile device withinthe airborne platform 102 a.

The process begins by synchronization of the surface based Antenna Array104 a with the mobile Airborne platform 102 a at step 902.Synchronization is itself a well known process. However, given the powerrestraints the current system is operating under, as well as the greatdistance between the airborne platform 102 a and the antenna array 104a, traditional synchronization protocols are woefully inadequate.Instead the system approaches the issue of synchronization with a novelmethod whereby randomized, or deterministically generated, beamformscontaining synchronization data are transmitted in a multitude ofdirections. This process and systems for synchronization of the airborneplatform's communication system and that of the surface based antennaarray 104 a will be described in more detail below in relation to FIGS.10A and 10B.

After synchronization the process progresses to step 904 where trainingof the communication system is performed. Training is required toproperly generate beamforms with correct directional signal propagationin order to reach the intended target. During training known symbols orpilots are transmitted and utilized by the receiver to generate weightsfor antenna amplitude and phase shifts in order to generate the properbeamform to respond to the original transmitter device. Training will bediscussed in more detail below in relation to FIG. 11.

After training is performed, the system may identify sources ofinterference, at step 906. Interference sources may include otherdevices operating within the same or similar frequency range. Since, insome embodiments, the system is operating in crowded radio spectrum, amultitude of devices may emit radio signals within the same frequencyrange. For unlicensed spectrum these could include Wi-Fi access points,cordless phones, microwaves, remote control devices, microwave ovens,and the like. These devices tend to be low powered devices, thereforeonly relatively close devices are typically considered sources ofinterference.

In addition to external devices being sources of interference, othersurface based antenna arrays and airborne platforms may be sources ofunwanted signals. The process may block all these sources ofinterference through null steering, at step 908. As noted before, inaddition to generating a beamform, one or more null spaces may begenerated with an antenna array 104 a. These null spaces may be orientedin order to “block out” the interference sources. Null steering will bedescribed in more detail below in relation to FIGS. 3 and 12.

After the generation of a null space, the process may progress to step910, where a directional beam may be transmitted (i.e., beamforming) tothe receiving device. As noted, beamforming may be accomplished throughthe selective weighing of amplitude and phase shifting of the signalprovided to each of the antennas within then antenna arrays. Weights, asnoted above, are calculated for each antenna during the training step.In addition to transmitting data via a beamform, the antenna array 104 amay likewise receive data at step 912. Details of beamform transmissionand receipt will be discussed below in greater detail.

Note that beamformers can be classified as either data independent orstatistically optimum, depending on how the weights are chosen. Thegeneration of weights, in some embodiments, is discussed above in somedetail in relation to system training processes. The weights in a dataindependent beamformer do not depend on the array data and are chosen topresent a specified response for all signal/interference scenarios. Theweights in a statistically optimum beamformer are chosen based on thestatistics of the array data to “optimize” the array response. Ingeneral, the statistically optimum beamformer places nulls in thedirections of interfering sources in an attempt to maximize the signalto noise ratio at the beamformer output.

After transmission and receipt of data, the process continues to step914 where an inquiry is made whether the airborne platform 102 a and thesurface based base station are out of range. If so, the process ends.Typically, this occurs as the airborne platform 102 a flies beyond thecoverage area of the surface based antenna array 104 a. In most casesthe airborne platform 102 a in communication with more than one surfacebased antenna array 104 a, thereby enabling the airborne platform 102 ato experience seamless data communication as it enters and exits thecoverage areas of multiple surface antenna arrays.

If the airborne platform 102 a is not out of range, however, the processcontinues to step 916 where an inquiry is made whether to update thesynchronization between the base station and the airborne platform 102a. Synchronization updates are necessary because the airborne platform102 a is constantly moving rapidly. The coverage of a beamform isrelatively limited. For example, beams could be as narrow as 5-10degrees. Thus, as the airborne platform moves, it may pass through thebeam coverage in approximately 20 milliseconds depending on the distancebetween the airborne platform 102 a and the surface based antenna array104 a. Thus optimally, the synchronization may occur every 5milliseconds, in some embodiments, in order to keep the directionalityinformation for beams current.

In addition to using time since last synchronization event to determineif an update is necessary, particular events may trigger asynchronization update. These events may include loss of contact betweenthe airborne platform 102 a and the surface antenna array 104 a, signaldegradation, and the like. If synchronization update is desired, thesystem may then return to step 902 where the synchronization process isrepeated. Otherwise, if synchronization updates are not required, theprocess may instead return to step 906 where interferences areidentified.

Below is provided a number of subsections detailing the individualsub-processes of the long range, wireless, broadband data communicationas described at FIG. 9. Note that the provided subsections are intendedto describe particular embodiments. Additional methods may be employedto accomplish some of these sub-processes, and it is entirely within thescope of the invention to utilize any logical permutations oralternative processes to complete the wireless broadband data delivery.

A. Synchronization of the Airborne Platform with Surface Antenna Array

The synchronization of the surface based antenna array 104 a with themobile device housed at the airborne platform 102 a, as indicated atstep 902 of FIG. 9, will now be discussed in greater detail.

In some embodiments of the broadband wireless communication system, asingle mobile device 102 a is capable of directly communicating withmultiple base stations 110 a via an Antenna Array 104 a. In conventionalwireless communication systems, Antenna Arrays 104 a periodicallytransmit synchronization signals on a single antenna in all directions.An omnidirectional transmission allows the base station 110 a tosynchronize with a mobile device in an airborne platform 102 aregardless of its position. If the base station 104 a insteadtransmitted signals using beamforming, those mobile devices 102 afalling within a null of the Antenna Array's 104 a transmission wouldnot be able to synchronize with the base station 110 a.

However, in the context communicating long distances with an airborneplatform 102 a, it is possible that an omnidirectional synchronizationtransmission by either the airborne platform 102 a or the base stationwould not reach the opposing transceiver with enough power to bediscerned over background noise. This may be particularly true if thereare power restrictions in place on maximum antenna power levels. Thisis, again, in some embodiments, due to the power envelope restrictionplaced upon transmissions within this spectrum by the FCC. As noted, thecommunication between airborne platform 102 a and base station requiresthe gain advantage of beamforming in order to operate in the unlicensedspectrum. Omnidirectional transmissions are simply too weak to span thedistance with sufficient signal strength in order to perceivable byeither the base station or the airborne platform's mobile device.

In order to overcome this power limitation, in some embodiments of thebroadband wireless communication system, the Antenna Array 104 a maytransmit synchronization signals using at least two antennas of thearray, using beamforming or other smart antenna technology to transmitsynchronization signals over a greater distance and at greater gain.While this technique effectively transmits synchronization signals overgreater distances, it also results in areas where synchronizationsignals are significantly diminished (e.g., in nulls).

In order to overcome this issue the system may, in some embodiments,transmit the beams in differing directions of signal propagationperiodically. There are two basic approaches for modifyingsynchronization signals in order to differ direction of signalpropagation: (i) random perturbation; or (ii) deterministicperturbation. Perturbation refers to changing the direction of the beamby altering the relationship of the signals driving the antennaelements.

Random perturbation is the modification of transmitted synchronizationsignals resulting in random variations of such signals. For example, onerandom perturbation technique is to randomly vary the phase ofsynchronization signals transmitted by one or more antennas of the basestation antenna array 104 a. For example, if four antennas are used forsynchronization signal transmission, the signals being transmitted byone or more of the four antennas being used may be varied in some aspect(e.g., phase, amplitude, and the like) resulting in a likely change inthe propagation of the synchronization signal.

Using deterministic perturbation, synchronization signals are varied ina manner other than random perturbation. For example, synchronizationsignals may be varied in a predetermined manner designed to move one ormore beams so as to reduce the likelihood that a mobile device 102 awould fall in a null and be unable to synchronize with the base station104 a. Any deterministic variance may be used, including, for example,varying synchronization signals a predetermined amount, varyingcharacteristics (such as phase, amplitude, and the like) ofsynchronization signals transmitted by each antenna, etc.

In this way, the mobile device in an airborne platform 102 a is likelyto fall within at least one of the randomized, or deterministic, beams.Likewise, each mobile device would be unlikely to fall in a null for anunreasonable period of time.

FIG. 10A illustrates one embodiment of the process of synchronizationutilizing randomized or deterministic beamform perturbations across atime domain, shown generally at 902A. This process begins at step 1002where randomized or deterministic beamform perturbations are generated.The beamforms are then sequentially transmitted with these differingdirectional signal propagation paths. The system then waits for a returntransmission at step 1004. The return response may then be utilized tocalibrate, at step 1006, the generation of future trainingtransmissions.

The system may exhibit symmetrical behavior, as well; a mobile devicelocated on an airborne platform 102 a may search for base stations inthe same manner. In these embodiments, the airborne platform 102 a maysend out randomized, or deterministic, beams in hopes of reaching a basestation.

Referring to FIG. 4, one implementation of a base station antenna array104 a includes multiple antenna elements that are used to transmitsynchronization signals. This base station antenna array 104 a formsmultiple beams 400, with nulls in between. By varying these beams 400using a deterministic perturbation, the propagation pattern may berotated so as to cover a larger area over a period of time. Likewise, arandomized perturbation could also be used to generate a similar result.

In addition to the perturbation techniques used, the performance ofsynchronization may be modified by varying the time intervals betweensuch perturbations. If the time interval is very short, then thespectral efficiency may be somewhat diminished as administrativeoverhead is increased; however, if the time interval is too long, thenmobile stations may have difficulty in synchronizing with a base stationin a timely manner. Perturbations may occur periodically, perturbationsmay occur randomly, or perturbations may occur upon the satisfaction ofone or more conditions. Further, perturbations are not required for eachtransmission—in some implementations, a synchronization signal isrepeated without perturbation for an interval before modification. Insome embodiments, perturbations occur after a predetermined timeinterval (e.g., 1-20 ms). In other implementations, perturbations occurafter every x frames, where x is a number greater than or equal to 1.

In addition, in some embodiments, the synchronization beam width may bewider than a communication beam, because the data contained within asynchronization signal is relatively little as opposed to acommunication data signal. In some embodiments, the synchronizationsignal includes a data header indicating base station direction andother pertinent data, which is followed by an instruction to respond.Once the mobile device receives the synchronization signal, includingthe response instruction, it may generate a return beamform signal whichis more narrowly defined and includes a higher gain.

Another technique that may be used to improve synchronization isillustrated at the process of FIG. 10B. Here the used spectrum is brokenup into N groups, where N is a number greater than 1 at step 1012. Forexample, in one implementation, spectrum is divided into one group foreach antenna. Then, either random perturbation and/or deterministicperturbation may be used for each of the N groups.

Further, the synchronization signals for two or more of the N groups maybe simultaneously transmitted, with beams formed in differing directions(either random or coordinated), at step 1014. In this manner, thelikelihood of a mobile station falling into a null for all N groups maybe significantly reduced or practically eliminated. Consider, forexample, a system using a 80 MHz RF channel. This 80 MHz RF channel maybe divided into, for example, 4 groups of 20 MHz each. A synchronizationsignal may be simultaneously transmitted for each of the 4 groups, withthe synchronization signal for each group oriented in a differentmanner. If the beam patterns are oriented in the manner shown in FIG. 4,then a mobile station within range is highly likely to fall in a beam ofone of the 4 groups at any given synchronization signal transmission.The beam patterns may be perturbed as discussed above, either in acoordinated manner, or randomly. In some embodiments, each groupcorresponds to a group of tones, where a tone is one carrier out of, forexample, 64, 128, 256, 512, 1024, 2048, 4096, or other number of tonesmaking up a communication channel.

In this process, the system then waits for a return transmission at step1016. The return response may then be utilized to calibrate, at step1018, the generation of future training transmissions.

Such a system provides benefit in that multiple beams may be sent, onvarying frequencies, within a singular time frame. Therefore the entiretime required to synchronize the base station and airborne platform 102a may be reduced. The drawback of such a method is that substantiallymore frequency spectrum is utilized in such a technique. This means thatdata communication is halted or reduced during synchronization periods.Further, this technique may require more computational power at the basestation 110 a than time division synchronization.

An Airborne platform 102 a may be configured to receive synchronizationsignals using multiple antennas, for example, synchronizing to one ofthe N synchronization groups (such as the strongest received signal)using one, two, or more antennas. The receive signals from two or moreantennas may be coherently combined to further extend thesynchronization range of the system. Furthermore, when multiplesynchronization signals are transmitted (such as when using the Nsynchronization groups discussed above), a mobile station may combinethe multiple groups coherently to increase the synchronization range, orcombine the received signals so as to cancel interference. In someembodiments, beamforming is performed on each group separately. In otherembodiments, beamforming is performed across some or all of the groupsand antennas at once.

Another method of synchronization, suitable for use in some embodiments,will now be discussed. This method relies upon stored data within theAirborne platform 102 a which indicates the location of all antennaarrays 104 a. Likewise, through elevation and navigational data, theAirborne platform 102 a is also aware of its own location. These twolocation values may be cross referenced to determine when the airborneplatform is in range of an antenna array 104 a and the direction thearray 104 a is located at. When the airborne platform is within range ofa surface based antenna array 104 a, the system may be configured togenerate a synchronization beamform from the airborne platform, basedupon location data, in order to initiate the communication. Theadvantage of such a deterministic system is that redundantsynchronization beam transmissions may be minimized in some instances.It is also possible that the system may be configured to attempt ahybrid approach where a synchronization beamform based upon locationdata is first attempted, and only if no response is received will thesystem revert to a randomized search as discussed in detail above.

B. Training of Beamform Weights

Now, the training of the surface based antenna array 104 a with theairborne platform 102 a, as indicated at step 904 of FIG. 9, will bediscussed in greater detail. As previously noted, beamformers can beclassified as either data independent or statistically optimum,depending on how the weights are chosen. The weights in a dataindependent beamformer do not depend on the array data and are chosen topresent a specified response for all signal/interference scenarios. Theweights in a statistically optimum beamformer are chosen based on thestatistics of the array data to “optimize” the array response. Someembodiments of the present system may rely upon data independentgeneration of weights; however, other embodiments, as will be discussedin more detail below, are statistical optimum beamformers.

The multiple side lobe canceller (MSC) is perhaps the earlieststatistically optimum beamformer. An MSC consists of a “main channel”and one or more “auxiliary channels”. The main channel can be either asingle high gain antenna or a data independent beamformer. It has ahighly directional response, which is pointed in the desired signaldirection. Interfering signals are assumed to enter through the mainchannel side lobes. The auxiliary channels also receive the interferingsignals. The goal is to choose the auxiliary channel weights to cancelthe main channel interference component. This implies that the responsesto interferers of the main channel and linear combination of auxiliarychannels must be identical. The overall system then has a response ofzero. In general, requiring zero response to all interfering signals iseither not possible or can result in significant white noise gain. Thus,the weights are usually chosen to trade off interference suppression forwhite noise gain by minimizing the expected value of the total outputpower.

Choosing the weights to minimize output power can cause cancellation ofthe desired signal, since it also contributes to total output power. Infact, as the desired signal gets stronger it contributes to a largerfraction of the total output power and the percentage cancellationincreases. Clearly this is an undesirable effect. The MSC is veryeffective in applications where the desired signal is very weak(relative to the interference), since the optimum weights will not payany attention to it, or when the desired signal is known to be absentduring certain time periods. The weights can be adapted in the absenceof the desired signal and frozen when it is present.

If the desired signal were known, then the weights could be chosen tominimize the error between the beamformer output and the desired signal.Of course, knowledge of the desired signal eliminates the need forbeamforming. However, for some applications enough may be known aboutthe desired signal to generate a signal that closely represents it. Thissignal is called a reference signal. Typically, a known set of pilots ortraining symbols are sent from a mobile station to a base station asreference signals; and the base station uses those known pilots ortraining symbols to calculate beamforming weights. The weights arechosen to minimize the mean square error between the beamformer outputand the reference signal.

The weight vector depends on the cross covariance between the unknowndesired signal present and the reference signal. Acceptable performanceis obtained provided this approximates the covariance of the unknowndesired signal with itself. For example, if the desired signal isamplitude modulated, then acceptable performance is often obtained bysetting the reference signal equal to the carrier. It is also assumedthat the reference signal is uncorrelated with interfering signals. Thefact that the direction of the desired signal does not need to be knownis a distinguishing feature of the reference signal approach.

Referring again to FIG. 1, when a mobile station, such as, for example,airborne platform 102 a or 102 b uses multiple antennas to performbeamforming, it is desirable to provide a mechanism such that theairborne platform 102 a or 102 b can effectively determine beamformingweights. In one implementation, the base stations 104 a, 104 b and 104 ctransmit known training symbols or code from the base stations to theairborne platform 102 a or 102 b. By receiving known signals, theairborne platform 102 a or 102 b can perform transmit and/or receivebeamforming using two or more antennas on the airborne platform 102 a or102 b to determine beamforming and/or null-steering weights.

For example, in one embodiment as illustrated at the process of FIG. 11,a base station 104 a transmits known data, such as, for example, acolumn from a Walsh, Golay, Hadamard, or Fourier matrix, from the basestation 104 a to the airborne platform 102 a at step 1102.

This training data (reference signal) is sent using one or more antennasfrom the base station 104 a, and preferably the data would be sent withspecific phases and gains on each of the antennas so as to steer a beamtowards the airborne platform 102 a as determined by the synchronizationcalibrations, as discussed above. Training data may be transmitted atany time and may be combined with existing signals. For example, asynchronization signal may be augmented with training data to facilitatesimultaneous synchronization and training.

At step 1104, the destination device receives the known data andutilizes it to generate weights. An example of how this calculation isperformed may be illustrated by the following equation: if known data Sis sent, where S is the training data, one could compute weights usingthe MMSE solution as such, W=(x^(H)x)⁻¹(x^(H)S), where x is the receiveddata with dimensions N×M, where N is the number of antennas and M is thenumber of samples, where samples is in time or tones or both.

Calculated beamforming and/or null-steering weights are retained for aperiod of time, such as, for example, for a predetermined time interval,until new weights may be calculated, and the like.

The process continues with a return transmission of known data beinggenerated at step 1106. Like the training calculation performed above,the original source may utilize the returned signal for generatingweights, at step 1108. The process for training may then end byreturning to step 906 of FIG. 9.

C. Null Steering

Now, the generation of a null space in response to detected interferencesources, as indicated at step 908 of FIG. 9, will be discussed ingreater detail.

In addition to performing beamforming, phases antenna array 104 a, suchas that found in the airborne platform 102 a, may perform null-steering.For example, it may be desirous for an airborne platform 102 a to steera null(s) toward one or more base stations 104 a, 104 b or 104 c thatare not presently being used. In this manner, the airborne platform 102a may reduce interference with those base stations 104 a, 104 b or 104c.

During beamforming a main lobe is produced together with nulls and sidelobes. As well as controlling the main lobe width (the beam) and theside lobe levels, the position of a null may be controlled. This isuseful to ignore noise in one particular direction, while listening forevents in other directions. Refer to FIG. 3 where a source ofinterference is illustrated existing below an airborne platform 102 a.

Here the airborne platform 102 a is configured to use unlicensedspectrum, thus it is possible that the airborne platform 102 a couldcause interference with, or be interfered with, by Wi-Fi networks,cordless phones, or other wireless services using unlicensed spectrum,as is prevalent in urbanized locations.

These devices project signal in an omnidirectional fashion in mostcases. However, these unlicensed devices must also abide by FCCguidelines and are thus generally low-power devices. Omnidirectionalprojected waves degrade exponentially as a matter of distance; this,plus the generally low power of the devices, means that the only sourceof interference for airborne platforms operating in unlicensed spectrumis typically the “close” devices directly below the airborne platform.By steering a null 302 directly under the airborne platform, thesepotentially interfering sources may be ignored.

Antenna Arrays 104 a, 104 b or 104 c not within the null are capable ofcommunicating with the airborne platform. Likewise, even if an AntennaArray 104 a is within the null, the beamforming of the Antenna Array 104a may have sufficient gain as to enable receipt of the data despitebeing within a null space.

One embodiment for the process for null generation may be seen inrelation to FIG. 12, shown generally at 908. In some other embodiments,a mobile station on an airborne platform 102 a identifies interferenceby measuring the received signals and identifying the signals anddirections of the signals that don't match expected training Theseinterference directions are received at step 1202. Then at step 1204,nulls are placed on those identified signals. Any signals that are fromother cells, not known, or not scheduled are treated as interference andnulls are placed on transmit and receive in those directions.

Furthermore, in some implementations, a time tail is used so that a nullis lessened over time, at step 1206. Thus, when a momentary interferenceis detected, a null may be placed for a period of time even if thedetected interference goes away. Tails are useful for interferingsignals that quickly turn on and off—by using a time tail, a null mayalready be in place when there is a sufficiently short break intransmission of the interfering signals. The process than ends byreturning to step 910 for FIG. 9.

While much of null steering has been discussed in relation toeliminating interference, an important note regarding null steering isthat this, in conjunction with very specific beamforming on thetransmitter side enables the transmitter to send data on the samefrequency, at full throughput, to multiple receivers simultaneously. Noknown transmission system is capable of this feat. It is only possiblethrough the very selective directional signal propagation (beams) beingsent to separate targets. Any reflection or bleed of a beam signal notintended for a given receiver is then viewed by the receiver asinterference and is ignored through null steering. This enables completespectrum re-use at 100% throughput.

FIGS. 15A and 15B are example illustrations of directional beamformingby an antenna array 104 a in range of a target and interference sourcein accordance with some embodiments. These figures illustrate a methodof null steering where the transmission target and an interferencesource are in relatively close proximity to one another. In such cases,it may be impractical to simply steer a null in the direction of theinterference source because this would effectively block out the targetas well. The target, in these example figures, is an airborne platform102 a. A wireless access point in an office building 1500 is the sourceof interference.

The interfering building 1500 is, in these example illustration,relatively close to the airborne platform 102 a target. The closeness ofthe target and interference source makes it such that any null steeredto the interference would also block out the target airborne platform102 a, which is an undesirable result. The example illustrationsindicate differing methods of dealing with this scenario.

In FIG. 15A, the beamform is directed such that maximum gain is directedto the target airborne platform. Processing may be utilized to separateout the interference to some degree, but inevitably some interference islikely to be received as well. The second method of FIG. 15B sacrificesabsolute gain in favor of maximizing the difference between gainsexperienced by the target and interferer. In this example, the beam isoriented askew of the target, but such that the interferer is receivedwith even less gain. Thus, while the target signal may be received withless perceived gain as compared to the example of FIG. 15A, thedifference between gain of the interference source and target is largerin the example of FIG. 15B. This may be thought of as a method of nullsteering whereby beam and null directions are considered in order tomaximize the difference between target gain and interference gain.

D. Beamforming

As noted previously, the unlicensed radio spectrum must comply with FCCregulation Part 15, which includes a maximum power envelope for thetransmitting device. Given the long range required for communicatingwith airborne platform, an omnidirectional transmission device, whenoperating within this power envelope, is undiscernibly over backgroundnoise at these great distances. Thus, the gain provided by beamformingis ideally suited to enable the operation of a system where unlicensedspectrum is utilized to communicate with airborne platform. Thus, fortransmissions and receipt of transmissions the system may, in someembodiments, rely upon beamforming, as indicated previously at steps 910and 912 of FIG. 9. Additionally, some embodiments may utilize otherfrequencies and are not necessarily constrained by this part of the FCCregulations. Even so, it may be desirous to improve signal gain in orderto overcome interference sources, and achieve substantially largereffective ranges.

The term beamforming derives from the fact that early spatial filterswere designed to form pencil beams in order to receive a signalradiating from a specific location and attenuate signals from otherlocations. “Forming beams” seems to indicate radiation of energy;however, beamforming is applicable to either radiation or reception ofenergy.

Systems designed to receive spatially propagating signals oftenencounter the presence of interference signals. If the desired signaland interferers occupy the same temporal frequency band, then temporalfiltering cannot be used to separate signal from interference. However,the desired and interfering signals usually originate from differentspatial locations. This spatial separation can be exploited to separatesignal from interference using a spatial filter at the receiver.Implementing a temporal filter requires processing of data collectedover a temporal aperture. Similarly, implementing a spatial filterrequires processing of data collected over a spatial aperture.

In some embodiments, a beamformer linearly combines the spatiallysampled time series from each sensor to obtain a scalar output timeseries in the same manner that an FIR (finite impulse response) filterlinearly combines temporally sampled data. Spatial discriminationcapability depends on the size of the spatial aperture; as the apertureincreases, discrimination improves. The absolute aperture size is notimportant, rather its size in wavelengths is the critical parameter. Asingle physical antenna (continuous spatial aperture) capable ofproviding the requisite discrimination is often practical for highfrequency signals since the wavelength is short. However, when lowfrequency signals are of interest, an array of sensors can oftensynthesize a much larger spatial aperture than that practical with asingle physical antenna. Note, each composite antenna represents asensor in some embodiments.

A second very significant advantage of using an array of sensors,relevant at any wavelength, is the spatial filtering versatility offeredby discrete sampling. In many application areas it is necessary tochange the spatial filtering function in real time to maintain effectivesuppression of interfering signals. This change is easily implemented ina discretely sampled system by changing the way in which the beamformerlinearly combines the sensor data. Changing the spatial filteringfunction of a continuous aperture antenna is impractical.

Beamforming takes advantage of interference to change the directionalityof the array 104 a whereby constructive interference generates a beamand destructive interference generates the null space. For example, iftwo airborne platform 102 a and 102 b use directional antennas such thatRF emissions radiate predominantly towards the surface, theninterference between two distant airborne platform 102 a and 102 b canbe abated. By using directional antennas, the communication system mayprovide increased spectral efficiency, possibly even permitting AntennaArrays 104 a, 104 b and 104 c to use the same frequencies or a smallersubset of frequencies.

As airborne platform 102 a, 102 b and 102 c fly, the relative directionfrom the airborne platform 102 a, 102 b and 102 c to the Antenna Arrays104 a, 104 b and 104 c changes. Accordingly, it is desirable to use beable to change the direction in which RF emissions radiate. Many suchtechniques are known in the art, for example, one or more directionalantennas may be used. These directional antennas may be mechanicallypositioned to transmit in the desired direction. Alternatively, a set ofdirectional antennas may be used, with a transceiver switching betweenthe available antennas to select a suitably-oriented antenna. Further,in some embodiments, a smart antenna array 104 a is used to dynamicallyvary directivity of transmission and/or reception.

Beamforming using a smart antenna array 104 a, during transmission, isaccomplished by controlling the phase and/or relative amplitude of thesignal at each transmitter, in order to create a pattern of constructiveand destructive interference in the wave front. Similarly, whenreceiving, information from different sensors is combined in such a waythat the expected pattern of radiation is preferentially observed (nullsteering).

The ability to beamform in this manner requires a minimum of twoantennas in the antenna array 104 a. In some embodiments, four antennasare located at each transceiver; both airborne platform 102 a and basestation. This directionality benefit of beamforming has been known bythose skilled in the art for some time. In general, beamforming may beaccomplished in a number of known ways, as is known by those skilled inthe art. For an example of a particular method of implementingdirectional beamforming, see: B. D. V. Veen and K. M. Buckley.Beamforming: A versatile approach to spatial filtering. IEEE ASSPMagazine, pages 4-24, April 1988.

An additional example of the mathematics behind beamforming may be foundin the article by Michael Leabman entitled Adaptive Band-Partitioningfor Interference Cancellation in Communication Systems. MassachusettsInstitute of Technology Press, February 1997.

Most array literature specifies spatial dependence in terms “angles”which is intuitive. It is also possible to define the wavenumbervariable {right arrow over (k)} which is a spatial vector in terms ofEuclidean space, where, |{right arrow over (k)}|=ω/c, ω being the radianfrequency (2πf), and c being the propagation speed in free space. Thus|{right arrow over (k)}|=ω/c=2πf/c=2π/λ has dimensions of 1/length,where the wavelength λ=f/c, and c=3*10⁸ m/s for radio waves. While thestandard angular representation does describe the response over theregion for all real signals, the full wavenumber space, or ‘virtual’space, is more useful in analyzing the consequences of spatial aliasing.

Now consider an array of N elements sampling an area of space where theelement locations are governed by [{right arrow over (z)}_(i), i=1, . .. , N]. The output from each sensor is input to a linear, time invariantfilter having the impulse response w_(i)(τ). The outputs of the filterare summed to produce the output of the array y(t),

${y(t)} = {\sum\limits_{i = 1}^{N}\;{\int_{- \infty}^{\infty}{{w_{i}\left( {t - \tau} \right)}{x\left( {\tau,{\overset{\rightarrow}{z}}_{i}} \right)}\mspace{11mu}{\mathbb{d}\tau}}}}$

Using the Fourier representation for a space-time signal, a plane wavex(t,{right arrow over (z)}_(i)) of a single frequency may be representedby a complex exponential in terms of a radian frequency ω, and vectorwavenumber {right arrow over (k)}:x(t,{right arrow over (z)} _(i))=e^(j(ωt−{right arrow over (k)}·{right arrow over (z)}) ^(i) ⁾

The array response to a plane wave is as follows:

$\begin{matrix}{{y(t)} = {\sum\limits_{i = 1}^{N}\;{\int_{- \infty}^{\infty}{{w_{i}\left( {t - \tau} \right)}{x\left( {\tau,{\overset{\rightarrow}{z}}_{i}} \right)}\mspace{11mu}{\mathbb{d}\tau}}}}} \\{= {\sum\limits_{i = 1}^{N}\;{\int_{- \infty}^{\infty}{{w_{i}\left( {t - \tau} \right)}{\mathbb{e}}^{j{({{\omega\; t} - {\overset{\rightarrow}{k} \cdot {\overset{\rightarrow}{z}}_{i}}})}}{\mathbb{d}\tau}}}}} \\{= {{\sum\limits_{i = 1}^{N}\;{\int_{- \infty}^{\infty}{{w_{i}\left( t^{\prime} \right)}{\mathbb{e}}^{{- {j\omega}}\; t^{\prime}}{\mathbb{e}}^{{- j}{\overset{\rightarrow}{k} \cdot {\overset{\rightarrow}{z}}_{i}}}{\mathbb{e}}^{{j\omega}\; t}{\mathbb{d}t^{\prime}}\mspace{14mu}{where}\mspace{14mu}\tau}}} = {t - t^{\prime}}}} \\{= {\sum\limits_{i = 1}^{N}{{w_{i}(\omega)}{\mathbb{e}}^{j{({{\omega\; t} - {\overset{\rightarrow}{k} \cdot {\overset{\rightarrow}{z}}_{i}}})}}}}}\end{matrix}$

letting,

${W(\omega)} = {{\begin{bmatrix}{w_{1}(\omega)} \\\vdots \\{w_{N}(\omega)}\end{bmatrix}\mspace{14mu}{and}\mspace{14mu}{E(k)}} = \begin{bmatrix}{\mathbb{e}}^{{- j}{\overset{\rightarrow}{k} \cdot {\overset{\rightarrow}{z}}_{i}}} \\\vdots \\{\mathbb{e}}^{{- j}{\overset{\rightarrow}{k} \cdot {\overset{\rightarrow}{z}}_{N}}}\end{bmatrix}}$

becomes y(t)=W⁺(ω)E(k)e^(jωt)

where W(ω,{right arrow over (k)})=W⁺(ω)E(k) is the frequency wavenumberresponse. The frequency wavenumber response evaluated versus direction{right arrow over (k)}, is known as the beampattern,

${{B\left( {a\left( {\theta,\phi} \right)} \right)} = {{W\left( {\omega,\overset{\rightarrow}{k}} \right)}❘_{\overset{\rightarrow}{k} = {\frac{2\pi}{\lambda}{a{({\theta,\phi})}}}}}},$

where a(θ, φ) is the unit vector in spherical coordinates.

The most widely used array, suitable for some embodiments, is a linearuniformly weighted array with N elements and an inter-element spacing ofΔz. Note, such an array is used by way of example, and other arraydesigns are considered within the scope of this invention.

If a frequency independent uniform weighting of 1/N is used, a frequencywavenumber response is arrived at:

${{{W\left( {\omega,k} \right)} = {\frac{1}{N}{\sum\limits_{n = {- \frac{N - 1}{2}}}^{\frac{N - 1}{2}}\;{\mathbb{e}}^{{- j}{\overset{\rightarrow}{k} \cdot {\hat{a}}_{z}}n\;\Delta\; z}}}},\mspace{14mu}{where}}\mspace{11mu}$${\overset{\rightarrow}{k} \cdot {\hat{a}}_{z}} = {k_{z} = \frac{\sin\;{c\left( {k_{z}\frac{L}{2}} \right)}}{\sin\;{c\left( {k_{z}\frac{\Delta\; z}{2}} \right)}}}$

Evaluating for

${k_{z} = {{{k}{\sin(\theta)}} = {\frac{2\pi}{\lambda}{\sin(\theta)}}}},$where θ is defined with respect to the angle to the z axis, abeampattern is calculated as:

${{B\left( {\omega,\theta} \right)} = \frac{\sin\;{c\left( {2\pi\;{\sin(\theta)}\frac{L}{2\;\lambda}} \right)}}{\sin\;{c\left( {2\pi\;{\sin(\theta)}\frac{\Delta\; z}{2\;\lambda}} \right)}}},\mspace{14mu}{{{where}\mspace{14mu} L} = {N\;\Delta\;{z.}}}$

Multiple beams may be utilized by each base station to communicate withmultiple aircrafts at one time, as is illustrated at FIG. 2. Forexample, a four antenna array 104 a may generate up to four simultaneousbeams and nulls. Likewise, any combination of beams and nulls adding tofour is possible. With more antennas on the array 104 a this number ofbeams is extendable to meet capacity requirements. Likewise, eachairborne platform may generate up to four beams, given the four antennadesign, in order to communicate with multiple base stationssimultaneously.

II. Antenna Array Design

Attention will now be drawn to FIGS. 5 to 7B which illustrate uniqueantenna array 104 a designs which enable proper coverage for long rangecommunications to an airborne platform 102 a. At FIG. 5, an AntennaArray 104 a is illustrated wirelessly communicating with an airborneplatform 102 a. The Airborne platform 102 a includes its own antennaarray 504.

The array 504 within the airborne platform 102 a may be of similardesign to that of the surface based Antenna Array 104 a. As illustratedthe array 504 may be contained within a belly mounted aerodynamic pod.Likewise, it is possible that the array 504 be in a recessed location onthe airborne platform, within the winglets, or within the front radardome.

In these embodiments, the Antenna Array 104 a may include four antennapanels 502 a, 502 b, 502 c and 502 d. By modulating the amplitude andphase of the signal at the base station 110 a and providing to themodulated signals to each of the antenna panels 502 a, 502 b, 502 c and502 d, respectively, a directional signal (i.e., a beam) 106 a isgenerated.

FIG. 6 provides a more detailed illustration of the Antenna Panel 502 a.The logic behind an optimized antenna is that to identify an airbornetarget (e.g., an airborne platform), the antenna is required to look atthe entire sky at 360° horizontal and 180° vertically. However, the gainrequired by the antenna is reduced the higher one looks vertically. Thisis due to the aircrafts geometry in relation to the antenna array 104 a.An airborne platform 102 a directly above the antenna array 104 a isrelatively close to the array 104 a (i.e., typically 10,000 to 35,000feet above the antenna array 104 a). However, an airborne platform 102 alow vertically, as seen from the antenna array 104 a, is a much greaterdistance from the array 104 a, often a hundred miles or more distant.FIG. 14 illustrates an example higher gain beamform 1402 and an examplelower gain beamform 1404 in order to better exemplify beam orientationsin relation to the horizon.

Thus, ideally, the antenna array 104 a is designed whereby the lowerimage area is viewed in higher gain. Typical antennas are currentlyavailable in high gain design. Most high gain antennas have widehorizontal beam width but very narrow vertical beam widths. An examplewould be a 2.4 GHz antenna with 17 dBi of gain that has +/−45 degreeshorizontal beam width, but only +/−10 degrees vertical/elevation beamwidth. Conversely, broad coverage antennas are also available; however,these antennas tend to have a much reduced gain value. For example,typical antennas at 2.4 GHz with 90 degrees vertical beam width wouldhave less than 3-5 dBi of gain. Further, other gain and coverage antennatypes are also considered within the scope of some embodiments.

The antenna design provided at FIG. 6 enables the antenna panel 502 a toprovide both high gain in the horizontal coverage area, and yet havefull coverage. This is accomplished by transmitting across more than onehigh gain, but limited coverage, antennas 602 a, 602 b, 602 c, 602 d to602 n. These high gain, but limited coverage, antennas 602 a consist ofa series of antenna elements wired in parallel. The presentlyillustrated high gain, but limited coverage, antennas 602 a are shownincluding six antenna elements; however, this is purely for illustrativepurposes. More or fewer antenna elements are considered as part of thisapplication. In general, the more antenna elements in parallel in asingular high gain, but limited coverage, antenna 602 a increases gainof the antenna, but also limits the coverage area. Thus, the high gain,but limited coverage, antennas 602 a may be selected as to provideoptimum gain to coverage requirements.

In addition to the high gain, but limited coverage, antennas 602 a, eachantenna panel 502 a may also include more than one broad coverageantennas 604 a, 604 b, 604 c, 604 d to 604 n. Typically these lower gainbut greater coverage antennas 604 a have few antenna elements (typicallybetween one and four antenna elements). Fewer elements reduce gain, butenhance coverage area.

The result of such an antenna design is very narrow but high gaincoverage along the horizon, and weaker but broader coverage on thehigher vertical angles. This comports well to the geometry of airborneplatforms flying near the Antenna Array 104 a, as discussed above.

The coverage may be further improved by squinting or skewing thecoverage angle of low gain or broad coverage antennas 604 a, as shown inthe comparison of FIGS. 7A and 7B. In FIG. 7A, the broad coverageantenna 604 a is shown including two antenna elements. The contact lead704 is coupled directly between the antenna elements resulting in acoverage area 702 centered around the midline of the broad coverageantenna 604 a. As noted above, broad coverage antennas 604 a typicallyinclude between one and four antenna elements. Squinting of the broadcoverage antennas 604 a is possible whenever it includes more than oneantenna element.

In FIG. 7B, by contrast, the contact lead 704 is coupled closer to oneof the antenna elements thereby altering the relative phases of thedrive signal to each element, resulting in a coverage area 702 which istilted above the midline of the broad coverage antenna 604 a. This isreferred to as “squinting” the antenna. By altering the phase of eachantenna element relative to others, this squinting can be varied to suitthe desired coverage area. Given that in the antenna panels 502 a thelower vertical coverage area is being viewed by the high-gain antennas602 a, there is no need for the broad coverage antennas 604 a to coverthe same viewing area. Thus these antennas may be squinted up to coverhigher vertical angles. Thus the broad coverage antennas 604 a providecomplete coverage of the airspace above the Antenna Array 104 a.

III. Load Balancing Between Base Stations

Furthermore, at seen in the example process of FIG. 13, a broadbandwireless communication system enabling data communications with airborneplatform 102 a and 102 b may be improved by balancing loads acrossmultiple base stations 104 a, 104 b and 104 c. Using beamforming, anairborne platform 102 a, instead of communicating with a single basestation 104 a, may be communicate with multiple base stations,simultaneously, by forming a beam directed towards base station 104 a,forming a beam directed towards base station 104 b, and then combiningthe results, as in step 1302.

Load balancing provides a number of benefits to the system. First ofall, it enables increased data transfer rates since no single basestation is likely to become overburdened. Likewise, by relying uponmultiple base stations, the system allows for higher burst throughput,as each base station may send data to the airborne platformsimultaneously.

Further, network fidelity is increased, because if there is a disconnectwith any given base station, the remaining base stations may compensateaccordingly. Lastly, by balancing loads between multiple base stations,transfer from one cell to another when the airborne platform moves outof the coverage area of a base station's antenna array 104 a is easierto perform, and there is no lapse in connectivity.

Consider, for example, the system shown in FIG. 2. An airborne platform102 a, using multiple antennas to perform beamforming, communicates withmultiple base stations 104 b and 104 c simultaneously, by forming a beam106 f directed towards base station 104 b and a beam 106 e directedtowards base station 104 c. In this manner, the airborne platform 102 acan significantly increase system capacity. Furthermore, usingbeamforming in this manner, beams 106 e and 106 f may be transmittedusing the same frequencies at the same time from the same antennaswithout interfering with one another, thereby increasing capacitywithout using additional spectrum.

In some embodiments, the airborne platform 102 a may dynamically adjustcapacity based on utilization, as indicated at step 1304. For example,the airborne platform 102 a may initially use a single beam 106 f tocommunicate with base station 104 b. When utilization increases (eitherat the base station 104 b or at the airborne platform 102 a), theairborne platform 102 a may add a second beam 106 e to communicate withbase station 104 c. The airborne platform 102 a may use the additionalcapacity in any manner, including, for example, by splitting utilizationbetween the base stations 104 b and 104 c, or by dividing load based onsome criteria such as overall number of communication channels ongoingat any given base station. Many network load-balancing techniques areknown in the art, and any such technique now known or later developedmay be used in this manner. The embodiment discussed above initiates andcontrols load balancing from a mobile station, such as airborne platform102 a; however, load balancing also may be initiated from a base station104 b or 104 c, as indicated at step 1306, or through any combination ofairborne platform and base stations operating in concert.

The load balancing implementations discussed above use two beams 106 eand 106 f; however, some implementations may provide for additionalbeams. For example, an airborne platform 102 a using N antennas may formup to N beams. Each of these beams may be directed towards a differentbase station. In some implementations, multiple beams are formed anddirected towards a single base station; however, in suchimplementations, when multiple beams are directed to a single basestation, each of the beam so directed, is configured to use differentfrequencies so as to avoid interference.

IV. Multiplexing Processing Elements

The processing capabilities necessary to perform null-steering and/orbeamforming, such as those techniques described above, are notinsignificant. Furthermore, it may be desirable to provide a commercialsystem that is scalable, for example, from handling a single 10 MHzchannel to a larger channel, such as, for example, 20 MHz, 40 MHz, 80MHz, or greater.

Typically, when a system is forced to handle N-times more bandwidth, itrequires N-times more equipment. For example, one approach to building ascalable system is to build a processing device capable of handling 10MHz, and by simply adding additional 10 MHz processing devices to scaleup. Thus, an 80 MHz bandwidth system would require eight 10 MHzprocessing devices. Furthermore, the antenna outputs from each of thedevices would be combined using one or more RF combiners/splitters foreach antenna. However, the use of combiners/splitters attenuatessignals, losing valuable gain.

An alternative approach to scaling from 10 MHz to 80 MHz of bandwidthwould be to increase the processing capabilities of the digital boardsuch that it is capable of processing the entire 80 MHz bandwidthchannel. Because processing capabilities required for 80 MHz ofbandwidth are significantly higher than that required for 10 MHz ofbandwidth, it is unlikely to be desirable or cost-effective to use asingle board with current technology. As processing technologies evolvehowever, such an embodiment may be readily utilized.

Instead, in some embodiments, a hybrid approach may be used to leveragethe benefits of each approach by combining the two techniques and addingan intermediate step. Instead of using multiple devices capable ofhandling a piece of the total available spectrum, the functions ofanalog radios and digital baseband processors are divided such that Xradios are used along with Y digital baseband processing devices.

One such scalable system may be designed by breaking up the bandwidthinto N groups. For example, four devices could be utilized to dividingan 80 MHz into 20 MHz groups for processing. In this embodiment, aseparate radio may be used for each digital processing device. Theresulting analog signals are combined (for transmit) or split (forreceive) by RF splitter/combiner, which is then coupled to the antenna.This arrangement may be replicated for each available antenna.

In another embodiment, as illustrated at FIG. 8, the Antenna (802 a, 802b, 802 c to 802 p) may instead couple directly to a Radio Frequency (RF)board including a down converter and an Analog to Digital (A-D)converter (804 a, 804 b, 804 c to 804 q). For example, assume that thesignal received by the antennas is 2.45 GHz, in some embodiments. The RFconverter may reduce the signal to a lower bit rate to enableprocessing, say 80 MHz. However, with an increase in antennas, the finalprocessing requirements are then 80 MHz times the N antennas present,for this example. This much data may be difficult for any givenprocessing unit to handle. Instead, in the present example, assume thatthe digital processors are capable of handling 20 MHz of bandwidth data.Thus the data streams must be divided into manageable parts forprocessing. This may be accomplished by a digital splitter 806 coupledto the Analog to digital converters (804 a, 804 b, 804 c to 804 q) whichmay split the data flow to each Digital Signal Processor (DSP) (808 a,808 b, 808 c to 808 r) for processing.

The problem with splitting the data is that it is a signal and thuscannot be simply split into time sections. Instead, in this embodiment,the digital splitter 806 may orthogonalize the signals utilizing a FastFourier Transformation (FFT) in order to split the signal among thevarious DSPs (808 a, 808 b, 808 c to 808 r).

A larger or smaller number of antennas (802 a, 802 b, 802 c to 802 p)may be used with the processing boards and radios as shown. For example,two antennas may be used with four digital processing devices (808 a,808 b, 808 c to 808 r) and four radios (804 a, 804 b, 804 c to 804 q).

Another embodiment for processing the data may rely upon fewer radios.For example, in some embodiments, a single radio is used. Thiseliminates the need for an RF splitter/combiner, thus reducingattenuation. However, to implement such a system, an additional step isused to break up the channel into smaller frequency groups beforedigital baseband processing. Instead of each radio handling a portion ofthe entire channel, the radio handles the entire channel, and thespectrum is divided before baseband processing by an intermediatedigital processing device.

The intermediate digital processing device may divide the channel intofrequency groups using several techniques, including by performing aHadamard or Fast Fourier Transform (FFT) on receive for eachantenna/radio after the data is digitized from analog-to-digital, and toperform a Hadamard or IFFT on each antenna/radio for transmit. Thegroups fill in the inputs to the IFFT/FFT and Hadamard. For example, todivide an 80 MHz channel into 4 groups on receive, 4 samples at 80 MHzfeed the FFT and produce 4 outputs, each output being a 20 MHz channel.Conversely, 4 groups of 20 MHz can be used to feed the digital-to-analogconversion on transmit, resulting in an 80 MHz signal.

In this manner, the number of analog radios may be reduced, while stillincreasing the number of digital processing devices that may beindependently varied as is necessary or desirable. Such a systemsignificantly reduces complexity and costs for base stations byeliminating redundant radios and other hardware components. Further, allof the disclosed systems are scalable, thus as bitrates increase, thesystems may be modified to meet the processing demands.

V. Dynamic Frequency Selection

In some embodiments of a broadband wireless communication system, mobiledevices such as those found in the airborne platforms may use variousportions of a communications channel. For example, a communicationchannel may be divided into N groups, with mobile devices capable ofusing any of the N groups. As a mobile device moves, for example, fromsector to sector or from cell to cell, interference and bandwidthutilization may vary. Accordingly, it is desirable in some embodimentsto dynamically vary frequency utilization.

For example, in one implementation, the mobile device is capable ofprocessing N groups of an 80 MHz channel, where each frequency group is80 MHz/N. Based on some criteria, such as, for example, measuredinterference, measured utilization, request from a base station, or thelike, the mobile device is capable of tuning its RF to a differentfrequency group. In some embodiments, multiple groups may be used at onetime. In such an implementation, a mobile device may be configured suchthat it is capable of choosing to not transmit on certain groups,preferably transmitting only on those groups having less interferenceand/or utilization.

In some implementations, it may be desirable for the mobile device to beable to use different frequencies and/or different groups on differentbeams. For example, if the mobile device is close to the base stationantenna array 104 a and less gain is needed, the mobile device 102 acould tune each antenna to a different channel so as to handle 80 MHz/Nbandwidth on each of N antennas, thus using all 80 MHz. Each antennawould handle a different 80 MHz/N frequency. This would enable a singlesystem to use all the antennas for beamforming on a smaller 80 MHz/Nchannel when gain and coverage is needed, or the system could processall 80 MHz by having each RF/antenna tuned to one of the 80 Mhz/Nchannels. As interference and/or utilization are detected, thoseaffected frequencies would not be used.

Some implementations use a combination of load-balancing and/or dynamicfrequency selection to provide constant quality of service (QoS) as amobile device embodied in an airborne platform 102 a passes from onebase station's antenna array 104 a to another.

VI. Radio Frequency Power Control

In addition, it is desirable, in some embodiments, in a broadbandwireless communication system, to use as little power as is necessary,to mitigate potential interference. One way to perform RF power controlon a mobile device is for a communicating base station 110 a to measurethe received signal level. This signal level may result from mobiledevice on an airborne platform 102 a transmission using multipleantennas or a single antenna. Based on this measurement, the basestation 110 a sends a message to the airborne platform 102 a indicatingwhether to increase and/or decrease its transmission power. Based onthis message, the communication device located on the airborne platform102 a adjusts the transmit power on the two or more antennas that it iscurrently using to communicate with the base station's antenna array 104a.

VII. Data Transfer Via Relay

In some embodiments, the presence of surface based antenna arrays may belacking, such as in the middle of the ocean. In these cases it may bepossible to extend the functional range of data communications byrelaying signals from one airborne platform 102 a to another. Typically,airborne platforms follow common flight paths, both over land and theoceans. The advantage of these flight paths includes reduction ofdistance by traveling closer to the poles. Likewise, regulations, suchas FAA regulations require set flight paths whereby the airborneplatform are within a particular distance of a landing location at anygiven time. Thus, at any given time, along these trans-ocean airways,any given airborne platform 102 a is likely within transmittabledistance to another airborne platform 102 a. This enables a givenairborne platform 102 a to transmit to another airborne platform alongthe flight path using any of the previously identified beamformingmethodologies. The receiving airborne platform 102 a may then relay thetransmission to another airborne platform 102 a, and so forth until anavailable surface based antenna array 104 a is reached. In this way,data communication may be maintained even in circumstances where nosurface based antenna array 104 a is within transmission range. In someembodiments, a tail located antenna array may be best situated tofacilitate communication between airborne platforms.

In order to further enable this form of trans-ocean relaying, maritimevessels including mobile devices may likewise be utilized as relaypoints. In such a way, it may be possible to extend data communicationcoverage even farther.

VIII. Adaptive Allocation Between Upload and Download

Another novel feature of some embodiments is the ability to adaptivelyallocate upload and download bandwidth allowances. Most dataconnections, with the Internet for example, have a fixed allocationbetween upload and download. Typically the upload (PC to Internet) isgiven less bandwidth than the download (Internet to PC). This reflectsthe direction that most of the data usually flows; typically from theInternet to computer user. Internet requests (upload) are typicallysuccinct. The usual ratio is 5 to 1, meaning the bandwidth set aside fordownload is 5 times greater than the bandwidth allocated for upload(Internet requests). Hence, when a person runs an Internet speed test,they might see a ratio like 1.5 Mbps download and 0.3 Mbps upload. Eventhough during the speed test there is no data being downloaded, theupload bandwidth is fixed and remains constant, always around 300 Kbps.This is done to be sure when the user of the Internet hits the “Enter”button to send a URL to the Internet, the request is not placed on holduntil the downloading data is complete. It makes the Internet connectionappear to be faster than it is.

To maximize throughput in both directions, some embodiments areconfigured to dynamically allocate bandwidth between upload anddownload. If there is no upload traffic, the entire 100 Mbps bandwidthis used for download. If there is no download, the entire 100 Mbps isused for upload. Furthermore, because the allocation is dynamic, ifthere is traffic both ways at the same time, the smaller-size datatraffic will get less bandwidth than the higher volume of data beingtransferred. This process optimizes the throughput in both directions.An Internet speed test will show 100 Mbps download and also 100 Mbpsupload. This is only possible because the throughput is fast enough thatit is not necessary to reserve or dedicate portions of the bandwidth forthe upload.

In some alternate embodiments, a particular portion of the bandwidth maybe reserved for, say, transmission of operational and safety data fromthe airborne platform to the surface. This enables these embodiments ofthe system to always transfer critical data regardless of load balances.Thus, even if every passenger on the airborne platform downloads a movieat the same time, it is possible that the system maintains some setbandwidth for crucial safety and operational data. All remainingbandwidth, however, may be dynamically allocated as discussed above.

For example, assume 20 Mbps of the total 100 Mbps bandwidth is reservedfor critical data transfers. Now assume that 30 gigabytes is beingdownloaded by the airborne platforms passengers. Likewise, 10 gigabytesof data is being uploaded by the passengers, as well. In such a case,the non reserved bandwidth of 80 Mbps may be allocated in a three to onesplit dynamically (i.e., 20 Mbps for uploads and 60 Mbps for downloads).

IX. Correction of Doppler Effect for Airborne Platform Beamforms

The Doppler Effect is an issue whenever substantial speeds are involved.In the case of beamforming, the Doppler Effect may alter the phase of atransmission, which may likewise influence the direction of signalpropagation. Thus, the Doppler Effect is typically seen as a significanthurdle to applying beamforming radio communications to airborneplatform.

A point-to-point radio returns a reply signal right back to the precisefrequency vector from which the communication originated. To give aradio mobility, such as is being performed by some embodiments, thesignal is returned to a different location (due to the movement/mobilityof the airborne platform) within a specified proximity to the originalsignal source. In the case of a moving object, the location of thesignal origin has changed by the time a reply is sent. So the respondingsignal has to search a bit for the location of the signal's originalsource. This searching takes a few more nanoseconds than apoint-to-point connection. Hence, in some of the embodiments the systemmay modify “time out” periods. In addition, the direction parameters ofthe signal are likewise modified to accommodate for phase shiftsattributable to the Doppler Effect. In some embodiments, thesemodifications to the direction parameters may depend upon directionalityof signal propagation and speed the airborne platform is traveling at.

In sum, systems and methods for wireless broadband data communicationare provided. While a number of specific examples have been provided toaid in the explanation of the present invention, it is intended that thegiven examples expand, rather than limit the scope of the invention.Although sub-section titles have been provided to aid in the descriptionof the invention, these titles are merely illustrative and are notintended to limit the scope of the present invention.

While the system and methods has been described in functional terms,embodiments of the present invention may include entirely hardware,entirely software or some combination of the two. Additionally, manualperformance of any of the methods disclosed is considered as disclosedby the present invention.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, modifications andvarious substitute equivalents, which fall within the scope of thisinvention. It should also be noted that there are many alternative waysof implementing the methods and systems of the present invention. It istherefore intended that the following appended claims be interpreted asincluding all such alterations, permutations, modifications, and varioussubstitute equivalents as fall within the true spirit and scope of thepresent invention.

What is claimed is:
 1. An antenna array for long distance wirelesscommunication between an airborne platform and a surface base station,the antenna array comprising: a higher-gain beamforming antennaconfigured to transmit to a base station and receive from the basestation, and further configured to form a more directional beamsubstantially closer to the horizon; and a lower-gain beamformingantenna configured to transmit to a base station and receive from thebase station, and further configured to form a less directional beamsubstantially below the horizon as compared to the more directionalbeam, wherein the lower-gain beamforming antenna has a gain less thanthe higher-gain beamforming antenna, wherein the less directional beamhas a larger width than the more directional beam, and wherein the lessdirectional beam and the more directional beam may be directedindependently.
 2. The system as recited in claim 1, wherein thehigher-gain beamforming antenna is configured to have a substantiallycomplete coverage area around the antenna array in the horizontaldirection.
 3. The system as recited in claim 1, wherein the higher-gainbeamforming antenna is configured to have a coverage area of between thehorizon and substantially an acute vertical angle below the horizon. 4.The system as recited in claim 3, wherein the substantially an acutevertical angle below the horizon is approximately 10 degrees.
 5. Thesystem as recited in claim 1, wherein the lower-gain beamforming antennais configured to have a substantially complete coverage area around theantenna array in the horizontal direction.
 6. The system as recited inclaim 1, wherein the lower-gain beamforming antenna is configured tohave a coverage area of between a substantially acute vertical anglebelow the horizon to approximately vertical.
 7. The system as recited inclaim 6, wherein the substantially an acute vertical angle below thehorizon is approximately 10 degrees.
 8. The system as recited in claim1, wherein the lower-gain beamforming antenna includes at least fourelements.
 9. The system as recited in claim 1, wherein the higher-gainbeamforming antenna includes at least four elements.
 10. A method forantenna array optimization for long distance wireless communicationbetween an airborne platform and a surface base station, the methodcomprising: forming a higher-gain directional beam, wherein thehigher-gain directional beam is spatially oriented between an airborneplatform and a surface base station, and wherein the higher-gaindirectional beam is oriented substantially closer to the horizon; and;forming a lower-gain directional beam, wherein the lower-gaindirectional beam is spatially oriented between an airborne platform anda surface base station, and wherein the lower-gain directional beam isoriented substantially below the horizon as compared to the higher-gaindirectional beam, wherein the lower-gain directional beam has a gainless than the higher-gain directional beam, wherein the lower-gaindirectional beam has a larger width than the higher-gain directionalbeam, and wherein the less directional beam and the more directionalbeam may be directed independently.
 11. The method as recited in claim10, wherein the higher-gain directional beam is configured to be formedwithin a substantially complete coverage area around an antenna array inthe horizontal direction.
 12. The method as recited in claim 10, whereinthe higher-gain directional beam is configured to be formed within acoverage area of between the horizon and substantially an acute verticalangle below the horizon.
 13. The method as recited in claim 12, whereinthe substantially an acute vertical angle below the horizon isapproximately 10 degrees.
 14. The method as recited in claim 10, whereinthe lower-gain directional beam is configured to be formed within asubstantially complete coverage area around an antenna array in thehorizontal direction.
 15. The method as recited in claim 10, wherein thelower-gain directional beam is configured to be formed within a coveragearea of between a substantially acute vertical angle below the horizonto approximately vertical.
 16. The method as recited in claim 15,wherein the substantially an acute vertical angle below the horizon isapproximately 10 degrees.
 17. An enhanced antenna array for longdistance wireless communication between an airborne platform and asurface base station, the antenna array comprising: a higher-gainbeamforming antenna, comprised of at least four elements, configured totransmit to a base station and receive from the base station, andfurther configured to form a more directional beam substantially closerto the horizon, wherein the higher-gain beamforming antenna isconfigured to have a coverage area of three hundred and sixty degreesaround the antenna array in the horizontal direction, and wherein thehigher-gain beamforming antenna is configured to have a coverage area ofbetween the horizon and a substantially acute vertical angle below thehorizon, and wherein the substantially an acute vertical angle below thehorizon is approximately 10 degrees; and a lower-gain beamformingantenna, comprised of at least four elements, configured to transmit toa base station and receive from the base station, and further configuredto form a less directional beam substantially below the horizon, whereinthe lower-gain beamforming antenna is configured to have a coverage areaof three hundred and sixty degrees around the antenna array in thehorizontal direction, and wherein the lower-gain beamforming antenna isconfigured to have a coverage area of between the substantially acutevertical angle below the horizon to approximately vertical, wherein thelower-gain beamforming antenna has a gain less than the higher-gainbeamforming antenna, wherein the less directional beam has a largerwidth than the more directional beam, and wherein the less directionalbeam and the more directional beam may be directed independently.
 18. Anenhanced antenna array for long distance wireless communication betweena surface platform and at least two base stations, the antenna arraycomprising: a higher-gain beamforming antenna configured to transmit toa first base station and to receive from the first base station, andfurther configured to form a more directional beam towards the firstbase station; and a lower-gain beamforming antenna configured totransmit to a second base station and to receive from the second basestation, and further configured to form a less directional beam towardsthe second base station, wherein the lower-gain beamforming antenna hasa gain less than the higher-gain beamforming antenna, wherein the lessdirectional beam has a larger width than the more directional beam, andwherein the less directional beam and the more directional beam may bedirected independently.
 19. The system as recited in claim 18, whereinthe higher-gain beamforming antenna is configured to have asubstantially complete coverage area around the antenna array in thehorizontal direction.
 20. The system as recited in claim 18, wherein thelower-gain beamforming antenna is configured to have a substantiallycomplete coverage area around the antenna array in the horizontaldirection.
 21. The system as recited in claim 18, wherein the lower-gainbeamforming antenna includes at least four elements.
 22. The system asrecited in claim 18, wherein the higher-gain beamforming antennaincludes at least four elements.
 23. An antenna array for long distancewireless communication between an airborne platform and a surface basestation, the antenna array comprising: a higher-gain beamforming antennaconfigured to transmit to an airborne platform and receive from theairborne platform, and further configured to form a more directionalbeam substantially closer to the horizon; and a lower-gain beamformingantenna configured to transmit to an airborne platform and receive fromthe airborne platform, and further configured to form a less directionalbeam substantially above the horizon as compared to the more directionalbeam, wherein the lower-gain beamforming antenna has a gain less thanthe higher-gain beamforming antenna, wherein the less directional beamhas a larger width than the more directional beam, and wherein the lessdirectional beam and the more directional beam may be directedindependently.
 24. The system as recited in claim 23, wherein thehigher-gain beamforming antenna is configured to have a substantiallycomplete coverage area around the antenna array in the horizontaldirection.
 25. The system as recited in claim 23, wherein thehigher-gain beamforming antenna is configured to have a coverage area ofbetween the horizon and substantially an acute vertical angle above thehorizon.
 26. The system as recited in claim 25, wherein thesubstantially an acute vertical angle above the horizon is approximately10 degrees.
 27. The system as recited in claim 23, wherein thelower-gain beamforming antenna is configured to have a substantiallycomplete coverage area around the antenna array in the horizontaldirection.
 28. The system as recited in claim 26, wherein the lower-gainbeamforming antenna is configured to have a coverage area of between asubstantially acute vertical angle above the horizon to approximatelyvertical.
 29. The system as recited in claim 23, wherein each thelower-gain beamforming antenna and the higher-gain beamforming antennainclude at least four elements.